1. Field of the Invention
This invention relates generally to a control system for estimating the tongue length of a trailer being towed by a vehicle and, more particularly, to a control system for estimating the tongue length of a trailer being towed by a vehicle using a hitch angle between the trailer and the vehicle, where the vehicle includes driver operated front wheel steering with or without computer controlled rear wheel steering.
2. Discussion of the Related Art
Automotive vehicles that employ coordinated front wheel steering and rear wheel steering systems are known in the art. Typically, in such coordinated vehicle wheel steering systems, the driver controls the steering of the vehicle""s front wheels and a computer-based on-board steering controller controls the steering of the vehicle""s rear wheels in response thereto. In one example, the computer controlled rear wheel steering system employs an electric motor driven rack and pinion rear wheel steering actuator.
Known coordinated front and rear wheel steering systems typically provide both xe2x80x9cin-phasexe2x80x9d rear wheel steering and xe2x80x9cout-of-phasexe2x80x9d rear wheel steering. In-phase rear wheel steering occurs when the rear wheels are turned at an angle directed to the same side of a longitudinal axis of the vehicle as the front wheels. Out-of-phase rear wheel steering occurs when the rear wheels are turned at an angle directed to the opposite side of the longitudinal axis of the vehicle as the front wheels. The on-board steering controller determines the rear wheel steering angle as a function of vehicle speed and the operator actuated front wheel steering. The system, in general, will provide out-of-phase rear wheel steering at low vehicle speeds to reduce the turning radius of the vehicle, and in-phase rear wheel steering at high vehicle speeds to increase directional stability.
As is well understood in the art, it is sometimes a difficult and complicated task to effectively back up a vehicle that is pulling a trailer. It is heretofore known in the art to employ the coordinated front and rear wheel steering system discussed above to assist a driver operating a vehicle pulling a trailer. Particularly, U.S. Pat. No. 6,292,094, issued Sep. 18, 2001 to Deng et al., assigned to the assignee of this application, and herein incorporated by reference, discloses a vehicle-trailer backing-up control system in connection with a computer controlled rear wheel steering system. The ""094 patent employs an algorithm that uses front wheel angle, vehicle speed, vehicle yaw rate and hitch angle to control the rear wheel steering angle to assist the operator in backing up the vehicle with the trailer.
The vehicle-trailer backing-up control system disclosed in the ""094 patent has been effective in assisting the vehicle operator when backing up a trailer. However, because trailers come in a variety of different lengths the performance of the backing-up control system can be improved by providing an input to the system that gives an estimation of the tongue length of the trailer. The algorithm in the ""094 patent uses a constant tongue length for trailers of all lengths.
In accordance with the teachings of the present invention, a control system is disclosed for estimating the tongue length of a trailer being towed by a vehicle in connection with a coordinated front and rear wheel steering system associated with the vehicle. The control system employs an algorithm that calculates an estimated hitch angle between the vehicle and the trailer based on an initial tongue length estimation, a front wheel steering angle, a rear wheel steering angle, a measured hitch angle, vehicle speed and vehicle yaw rate. The estimated hitch angle is compared to the measured hitch angle to generate a hitch angle error signal that is converted to a tongue length error signal by a PID controller. The tongue length error signal is subtracted from the estimated tongue length to give a corrected estimated tongue length for a next computation period. After a few seconds of processing, the hitch angle error signal will be nearly zero and the tongue length error signal will be nearly zero, and thus the corrected tongue length will be the actual tongue length of the trailer.
Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.